1. Field of the Invention
The present invention relates, in general, to a system for the external fixation of a boney skeleton and, more specifically, to a positive locking, orthogonally adjustable external fixation system which allows a plurality of components to be connected at each adjustment node.
2. Background Art
In the practice of medicine, it is sometimes desirable to treat certain injuries or conditions with a system including an external frame that is attached to the boney skeleton with threaded and/or smooth pins and/or threaded and/or smooth and/or beaded wires. Such systems are commonly referred to as orthopedic external fixators or external skeletal fixators. These external fixators may be utilized to treat acute fractures of the skeleton, soft tissue injuries, delayed union of the skeleton when bones are slow to heal, nonunion of the skeleton when bones have not healed, malunion whereby broken or fractured bones have healed in a malposition, congenital deformities whereby bones develop a malposition, and bone lengthening, widening, or twisting, etc.
External fixator frames vary considerably in design and capabilities, and may include multiple or single bars or rods, a plurality of pins or wires joined to the boney skeleton, and a plurality of clamps or connectors for adjustably securing the pins or wires to the bars or rods. The pins or wires may extend completely through the boney skeleton and out each side of the limb or may extend through the boney skeleton and out only one side of the limb. Pins which extend completely through the boney skeleton and out both sides of the limb are commonly referred to as "transfixation pins." Pins which extend through the boney skeleton and out only one side of the limb are commonly referred to as "half pins." Materials for frames also vary, including metals, alloys, plastics, composites, and ceramics. External fixators vary in their ability to accommodate different spatial relations between each pin and bar, etc.
External fixation is commonly used for fractures. Fractures which involve more than two major fragments are referred to as segmental fractures. Some external fixation systems with adjustment means primarily confined to either end of the external fixator cannot treat intermediate or intercalary fragments with the same adjustability as either terminal fragment. Such external fixation systems may include outrigger type pin clamps used to secure intermediate fragments without the same adjustability as given the terminal fragments. Malreduction of fracture fragments can require additional surgery to reposition, or if left uncorrected can lead to delayed or nonunion or to malunion with impaired or symptomatic function.
External skeletal fixation is accomplished by secure coupling of two or more pins or wires to each major bone fragment and attachment of these same pins or wires to a supporting frame. The exact location and orientation of these wires and pins are determined by the physician considering anatomic and mechanical factors. To accommodate the sometimes varied position and orientation of these pins and wires, external fixation systems have a variety of adjustment means with varying degrees of adjustability and versatility. Adjustment means of some systems use ball joints which permit unrestrained rotation in three planes but make adjustment in a single degree of freedom difficult since loosening the ball joint clamp to improve one rotation permits loss of position of formerly correctly reduced rotations. Additionally, ball joints depending only on stiction friction are prone to slippage with subsequent loss of position. In fact, it has been recommended that such ball joints be filled with a glue which when set would prevent slippage and loss of position. Other adjustment means include a cylinder pair which when loosened allow two simultaneous motions, translation and rotation. Again, individual adjustment is difficult or impossible and most cylinder pairs rely on stiction friction. In these cylinder pairs, the holding power of the clamp will also be a function of the coefficient of friction of the two parts.
Adjustment means utilizing mechanically constrained surfaces such as radial splined faces provide positive locking of parts. Holding power relies more on geometry of mating parts and shear strength of constituent materials. Different systems incorporate mechanically constrained clamping mechanisms to different extents, including stiction friction ball joints, radial face splines on two of three rotations with the remaining rotation controlled by a stiction friction cylinder pair in combination with a translation, and three independent adjustments utilizing mating radial splined faces. Such adjustment means provide for independent adjustment of different rotations and also positive locking by virtue of mechanically constrained couplings.
In the course of treatment with external fixation, it is sometimes desirable or preferable to translate one or more bone fragments or to lengthen bones along an axis parallel to the axis of an external fixator bar. During such controlled translation or movement, it is desirable to maintain or control the other spatial relations of each fragment.
Ettinger, U.S. Pat. No. 2,250,417, issued Jul. 22, 1941, discloses an orthopedic external fixator for fracture reduction and retention including an elongated bar, a plurality of elongated threaded pins for transfixing bone elements, a first connector or head attached to one end of the bar for joining a pair of the pins to the bar, and a second connector or sleeve slidably positioned on the bar for connecting another pair of the pins to the bar. A portion of the bar is externally threaded and two nuts are screwably mounted on the bar, one on either end of the sleeve, so that proper rotation of the nuts will cause the sleeve and associated pins to move along the bar. The bar has either a circular cross section with a longitudinal keyway for receiving a key of the sleeve, or a square cross section with rounded, threaded comers in which case the sleeve is provided with a square bore to hold the sleeve against rotation on the bar.
Anderson, U.S. Pat. No. 2,391,537, issued Dec. 25, 1945, discloses an orthopedic external fixator for fracture reduction including a pair of hollow tubes telescopically joined together, a plurality of pins for transfixing bone elements, a first fixation unit slidably mounted on the first tube for connecting a pair of the transfixion pins to the first tube, and a second fixation unit attached to the end of the second tube for connecting a pair of the transfixation pins to the second tube. The second tube is telescopically mounted within the first tube. A threaded adjusting shaft is mounted within the tubes and can be manually rotated by way of a wrench head located at the outer end of the second tube. Rotation of the shaft causes a nut nonrotatably located within the second tube to move longitudinally along the shaft. Coil springs located within the tubes on either side of the nut transfer longitudinal movement of the nut to the tubes while permitting a certain desired yielding and eliminating any perfectly solid and hard contact.
Mears, U.S. Pat. No. 4,620,533, issued Nov. 4, 1986, discloses an orthopedic external fixator including a plurality of transfixation pins, an elongated bar, and a plurality of pin-to-bar clamps for adjustably attaching the pins to the bar. The pin-to-bar clamps including articulating balls for holding the pins and the bar when thumbscrews or the like are tightened. In addition, Mears discloses a bar-to-bar clamp for allowing a first elongated bar to be clamped relative to a second elongated bar.
Gotzen et al., U.S. Pat. No. 4,662,365, issued May 5, 1987, discloses a device for the external fixation of bone fragments including an elongated supporting bar, a plurality of bone pins, and a plurality of clamp assemblies for attaching the pins to the bar.
Nothing in the known prior art discloses or suggests the present invention. More specifically, nothing in the known prior art discloses or suggests a skeletal fixation system including a spool component for attachment to a bar; and an intermediate component for fixed attachment to the spool component and for joining at least one pin to the spool component, the intermediate component including pin receiving means for receiving one pin and intermediate component attachment means for allowing fixed attachment to another intermediate component.